Concrete slabs (e.g. formed of Portland cement) are employed in a variety of applications such as dwelling foundations. In applications such as roads, airport runways and warehouse floors the slabs may also form the exposed surface to which load is directly applied.
Typically slabs are formed by:                grading the “native” soil;        compacting the native soil and/or adding crushed rock, to form a top layer (referred to as a “sub-base”) which may have a higher shear strength than the native soil;        installing formwork about the sub-base to define the perimeter of the slab;        filling the formwork with wet concrete; and        allowing the concrete to set.        
Alternatively, pre-cast slabs may be laid upon sub-base.
Larger areas, such as roads and runways, are typically formed of a pavement made up of multiple slabs. The multiple slabs may be poured simultaneously (and separated by suitable temporary or permanent formwork). Alternatively, each slab may be poured after its neighboring slab has set. Either way there is a defined boundary between the slabs.
In use, load applied to the slab (e.g. by car driving along the roadway including the slab or a person standing on a carpet floor supported by the slab) is in turn applied the underlying soil.
Concrete is weak and brittle in tension. A load applied to a concrete slab at a point of the slab inadequately supported by the soil may cause the slab to crack. The slab may be inadequately supported (by way of example) due to the load being excessive or the soil having subsided away from the load point.
Cracking can occur at the peripheral margins of a slab (and particularly at the adjacent margins of adjacent slabs) due to “pumping”. When a slab is formed it typically takes on a slightly dished shaped due to differential rates of setting within the body of concrete. This is sometimes referred to “curling”. The dished shape leads to a lower contact pressure (or in extreme cases a cavity) at the interface between slab and soil about the slab's peripheral margins. In turn this leads to relatively more ground water coming and going from the particulate matter under these peripheral margins. This water movement tends to “pump” soil away and so exacerbate the problem.
Cracking followed by ongoing loading usually leads to an accelerated rate of deterioration. Even if the crack is not a full thickness crack, the load dispersing characteristics of the slab are compromised. A load applied to either of the slab portions defined by the crack is concentrated on the soil underlying that slab portion rather than being more evenly distributed over the soil underlying the entire original slab. This concentrated loading usually leads to accelerated soil subsidence, etc.
In the past, cracked and sunken concrete has been repaired by injecting material into the underlying soil and adhesively attaching members to span the crack. The present inventors have recognised that these existing approaches are problematic. Often the soil continues to subside and the members come away from slab portions, leading to a further similar failure. Sometimes too much material is injected, leading to a raised portion in the slab.
Various aspects of the invention aim to provide improvements in and for treating particulate and connecting slab portions, or at least to provide alternatives for those concerned with treating particulate and connecting slab portions.
It is not admitted that any of the information in this patent specification is common general knowledge, or that the person skilled in the art could be reasonably expected to ascertain or understand it, regard it as relevant or combine it in any way at the priority date.